1. Field of the Invention
The present invention generally relates to integrated circuit design, and more particularly to damascene fabrication using sacrificial metal spacers to aid in the fabrication process.
2. Description of the Related Art
Dual damascene processing in soft, non-silicon containing intermetal dielectrics, such as SiLK®, available from Dow Chemical Company, NY, USA, or FLARE®, available from Honeywell, NJ, USA. (both materials are polyarylenes (PAE)) is extremely difficult at sub 0.25 micron dimensions because of etch bias, undercut corner erosion, etc., and other problems frequent during RIE processing. Additionally, the traditional argon sputter cleans resputtered PAE into the via bottom and onto the underlying metal (i.e. copper or tungsten) surface, resulting in degraded contact interface properties. Although only argon sputtering is given as an example, all methods of directional sputter cleaning, including reactive ion etching (i.e. hydrogen doped) methods are associated with these problems. PAE-type materials are much softer than oxides, and have much lower thermal conductivity, and are not oxygen or water diffusion barriers. Therefore, in general, they have much worse dielectric properties than oxide.
Conventional methods of performing a dual damascene process is through multiple photoresist mask and etch steps. Here, a single level photoresist profile is formed on a layer deposited dielectric and a via pattern is formed by etching to a first interlevel in the dielectric material. At this point in the process the via is only partially etched. The photoresist is then stripped and a second single layer photoresist profile is formed on the dielectric surface to form an interconnect pattern to a second interlevel in the dielectric material. The interconnect is then formed by etching. Coincident with etching the interconnect, the via is etched such that interconnects in underlying substrate layers are exposed to allow electrical contact. However, aligning the photoresist profiles is a problem using this method. For example, if the two photoresist profiles are not aligned correctly, then intersecting features in the dielectric material will be misaligned. That is, a conductive line associated with the first photoresist pattern may not correctly intersect a via associated with the second photoresist profile. These alignment errors can be corrected by making the intersecting features oversized, but this takes away from the overall goal of reducing the size of connecting lines and vias. Thus, alignment problems reduce yields, and increase cost and the complexity of integrated circuit processes.
The trench and via profiles are greatly affected during dual damascene processing, due to the poor etching selectivity between the photoresist and the low dielectric constant dielectrics (low k dielectrics) while oxygen plasma removes the photoresist layer. Moreover, the low k dielectrics fill the gaps between the wiring lines in order to prevent parasitic capacitance, which occurs when the distance between subsequent wiring lines is reduced. Thus, in order to avoid the problems associated with conventional dual damascene manufacturing techniques, complicated processes and structures are implemented.
Even proposed solutions to these rather complex processes, such as the process described in U.S. Pat. No. 6,017,817, issued to Chung, et. al., “Method of Fabricating Dual Damascene,” the complete disclosure of which is herein incorporated by reference, does not provide an adequate solution to the problem of eliminating the PAE sputtering into the via bottom. Rather, these processes merely aim to reduce the effective capacitance of the low k dielectrics. In fact, these conventional techniques offer little, if any, solutions to such problems as etch bias and undercut corner erosion in the integrated circuit. Furthermore, the conventional processes do nothing to improve degraded contact interface properties due to the PAE sputtering into the via bottom.
Therefore, there is a need for a new and improved technique of damascene processing which overcomes the limitations of the conventional designs, and which improves the damascene process window, and/or eliminates the PAE sputtering into the via bottom by using a deep etch process.